Field of the Invention
The present invention relates to a steel material, a material processing method, and a material processing apparatus.
Description of the Related Art
A magnetic field application method as a structure control technique to improve the mechanical property, corrosion resistance, and functionality of iron-based metallic materials is known. JP-A-2001-234240 and JP-A-2000-328143 describe controlling a structure through magnetic field application in a temperature region no greater than the magnetic transformation point of a steel material.
JP-T-2009-510256 discloses a technique to suppress degradation through application of ultrasonic impact from a structural material surface.
In the techniques of the related art, structures are controlled by allowing the diffusion to simultaneously proceed with magnetic field application, and the techniques require heating and maintaining a temperature range in which crystal grain growth can occur. The ultrasonic impaction is effective at reducing the residual stress on a material surface, but involves difficulties in structure control.
Desired for controlling the structure of a steel material is a technique that can be implemented under as low a temperature as possible. Magnetic field application predominantly acts on the ferromagnetic phase, and enables crystal grain growth in the ferromagnetic phase along the magnetic field direction. Ultrasonic application is effective as a technique that induces dislocation or defect migration.
Ferromagnetic crystal grain growth increases the crystal grain size, and lowers mechanical property and corrosion resistance. There accordingly is a need for a technique that enables reducing residual stress while improving mechanical property and the corrosion resistance.